Combustors are commonly used in industrial and power generation operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, turbo-machines such as gas turbines typically include one or more combustors to generate power or thrust. A typical gas turbine includes an inlet section, a compressor section, a combustion section, a turbine section, and an exhaust section. The inlet section cleans and conditions a working fluid (e.g., air) and supplies the working fluid to the compressor section. The compressor section increases the pressure of the working fluid and supplies a compressed working fluid to the combustion section. The compressed working fluid and a fuel are mixed within the combustion section and burned to generate combustion gases having a high temperature and pressure. The combustion gases flow to the turbine section where they expand to produce work. For example, expansion of the combustion gases in the turbine section may rotate a shaft connected to a generator to produce electricity.
The combustion section may include one or more combustors annularly arranged between the compressor section and the turbine section. Various parameters influence the design and operation of the combustors. For example, higher combustion gas temperatures generally improve the thermodynamic efficiency of the combustor. However, higher combustion gas temperatures also promote flame holding conditions in which the combustion flame migrates towards a downstream end of the fuel nozzles, possibly causing accelerated damage to the nozzles in a relatively short amount of time. In addition, higher combustion gas temperatures generally increase the disassociation rate of diatomic nitrogen, increasing the production of nitrogen oxides (NOX). Conversely, a lower combustion gas temperature associated with reduced fuel flow and/or part load operation (turndown) generally reduces the chemical reaction rates of the combustion gases, increasing the production of carbon monoxide and unburned hydrocarbons.
In a particular combustor design, the combustor includes a cap assembly that extends radially across at least a portion of the combustor. A plurality of tubes is radially arranged in one or more tube bundles across the cap assembly to define a flow path for the compressed working fluid to flow through the cap assembly and into a combustion chamber. Fuel supplied to a fuel plenum inside the cap assembly may flow into the tubes through one or more fuel injection ports that extend radially through each or some of the tubes. The fuel and compressed working fluid mix inside the tubes before flowing out of the tubes and into the combustion chamber.
Although effective at enabling higher operating temperatures while protecting against flame holding and controlling undesirable emissions, the tube bundles present several manufacturing challenges due to the number of individual components required to form the fuel nozzle assembly and the overall complexity of the design. As a result, the complexity of the design generally corresponds to additional costs to manufacture the tube bundles. Therefore, an improved fuel nozzle that is less complex and/or less expensive to manufacture than current designs while promoting flame stability, and/or while reducing undesirable emissions over a wide range of combustor operating levels would be useful to the gas turbine industry.